This invention relates to a device for controlling the injection timing of fuel injection pumps in internal combustion engines. Such pumps are controlled to effect the injection of fuel into each cylinder of an internal combustion engine at a point in the cycle of the engine which is in advance of the top-dead-centre position of the respective piston in that cylinder, the amount of this advance being commonly expressed as the "advance angle" through which the engine crankshaft or flywheel rotates, after the injection of fuel into a cylinder, in order for the respective piston to reach the top-dead-centre position in that cylinder.
More particularly, the present invention relates to an electronic injection timing control device for a fuel injection pump in an internal combustion engine, in which the variation of the fuel injection timing is controlled in dependence upon a number of operating parameters of the engine.
In previously known fuel injection pumps the injection timing of the pump is controlled by a centrifugal governor responsive to the rotational speed of the shaft of the engine, the advance angle of the fuel injection being determined by the equilibrium position achieved by the governor. Such a centrifugal governor acts on the injection pump either directly or through a servo-control of the mainly hydraulic type. In modern engines with the need for low pollution of the atmosphere it is necessary to control the advance angle not only in dependence upon the rotational speed of the engine, but also in dependence upon other operating parameters, such as the temperature of the engine exhaust gases, the manifold pressure, or again, in the most elaborate systems, the chemical composition of the exhaust gases themselves.
For this purpose an electronic processing circuit is used, controlled by transducers which provide signals corresponding to the various parameters, the circuit giving an output signal which controls the variation of the fuel injection timing. This output signal must therefore be a function of the required advance angle of the fuel injection, and controls, usually through a proportional electrovalve, a metered flow of hydraulic fluid to an actuator which displaces axially a helically splined sleeve interconnecting the drive shaft of the pump shaft and a driving shaft, to vary the angle between these shafts until, when the optimum advance angle is reached, the parameters which control the system attain such values as to reduce the output signal to zero and therefore reduce or annul the flow of hydraulic fluid to the actuator.
This method of injection timing control is not very fast, due to the slow responses of the operating parameters of the engine to a variation of fuel injection timing, and moreover this method can cause instability in the system, because of the number of parameters involved and the sometimes strongly non-linear nature of their variations.
An object of this invention is to circumvent the aforementioned disadvantages by providing an electronic injection timing control device for a fuel injection pump which is of fast response and of high stability.